Conventionally used as a typical light-emitting device are a light emitting diode (LED), a vacuum fluorescent display (VFD), a fluorescent lamp, an incandescent lamp, or the like.
In a field of a display using LED (serving as the light-emitting device), an LED which emits blue light has been developed. Since red, green, and blue LEDs have been lined up, it is possible to carry out a full-color display. Thousands of three-color LEDs are provided in most of existing supersized full-color screens.
In addition, used as another existing displays are a CRT (Cathode-Ray Tube) display, a plasma display, a liquid crystal display, or the like.
The CRT display usually has three electron guns built-in. Three electron beams shot by the three electron guns are directed to a face glass of the display, and causes fluorescent materials, which are applied on a back surface of the face glass, to emit light. This allows the CRT display to carry out an image display. Moreover, basically, each pixel in the plasma display is partitioned by partition walls. Mercury argon gas, xenon gas, or the like is sealed within each partitioned pixel. That is, it is possible to say that thousands of extremely small fluorescent tubes are provided within a panel of the plasma display.
The liquid crystal display is basically arranged so as to include two glass plates, and a liquid crystal layer provided between the two glass plates. The liquid crystal layer is made by pouring liquid crystal in a gap between the two glass plates. The liquid crystal display carries out the image display by applying a voltage across the liquid crystal layer sandwiched between the two glass plates so that transmittance of the liquid crystal layer is controlled.
By the way, conventionally, a strain gage is mainly used as a stress sensor which measures stress exerted on architectural structures, or the like. The strain gage measures the strain by utilizing a physical phenomenon in which a resistance value of an electric resistor changes in response to the strain applied to the electric resistor.
However, the conventional light-emitting devices such as the fluorescent lamp, the vacuum fluorescent display, or the incandescent lamp respectively have the following problems.
That is, since the fluorescent lamp uses mercury, it is impossible to avoid environmental problems. Moreover, the vacuum fluorescent display has a triode vacuum tube structure composed of a positive electrode, negative electrode, and a grid, thereby giving rise to the complexity of the structure. Furthermore, since the incandescent lamp emits the light based on a heat emission obtained by heating up a filament in a glass bulb, the incandescent lamp has a short life span and has low crashworthiness.
The displays using the conventional light-emitting device have the following problems.
Namely, in the case where the LED is used as the light-emitting source of the full-color screen, the image display on the screen is carried out by thousands of dot emissions. That is, the image displayed on the screen is an aggregate of light-emitting dots. As such, it is difficult to improve a quality of the image displayed.
Moreover, since the CRT display structurally requires a glass tube hermetically sealed under high vacuum, it is complex in structure, it becomes large in volume, and it is impossible to save weight. In addition, another problems arise that the crashworthiness is low and there is a high possibility that the CRT display is destroyed by heat.
Furthermore, some plasma display uses mercury gas, thereby giving rise to a problem relating to environmental protection. Moreover, since the liquid crystal display uses the fluorescent tube as the light-emitting source, it has a problem relating to environmental protection like the plasma display does.
Moreover, the strain gage serving as a conventional stress sensor has the following problem. That is, a single strain gage can measure the stress only at a specific point of measuring object. In order to measure a stress distribution state of the measuring object, a plurality of strain gages are required. This is the problem which the strain gage has.
By the way, Japanese unexamined patent publication No. 49251/2001 (Tokukai 2001-49251, published on Feb. 20, 2001) has proposed a novel stress light-emitting material which emits the light in response to a deformation due to mechanically applied external force. The present inventors have attempted to utilize the stress light-emitting material to solve the conventional problems.